ES2629026T3 - Method and device for the preparation of expanded microspheres - Google Patents

Abstract

A method for the preparation of expanded thermoplastic microspheres from unexpanded thermally expandable thermoplastic microspheres comprising a thermoplastic polymer shell encapsulating a blowing agent, said method comprising: (a) feeding a suspension of such expandable thermoplastic microspheres in a medium liquid in a heating zone; (b) heating the suspension in the heating zone, without direct contact with any fluid heat transfer medium, so that the expandable microspheres reach at least a temperature at which they would have begun to expand at atmospheric pressure and maintaining a pressure at the heating zone high enough so that the microspheres in the suspension do not fully expand; and, (c) withdrawing the expandable microsphere suspension from the heating zone to a zone with a pressure low enough for the microspheres to expand.

Description

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DESCRIPTION

Method and device for the preparation of expanded microspheres

The present invention relates to a process for producing expanded thermoplastic microspheres and, therefore, to a device.

Thermally expandable microspheres are known in the art and are described in detail in, for example, US Pat. No. 3615972. Various degrees of expandable microspheres, which have different expansion temperatures, are commercially available from AkzoNobel under the trademark ExpancelTM, both in the form of dry free flowing microspheres and in an aqueous suspension of microspheres.

Such expandable microspheres comprise a blowing agent encapsulated within a thermoplastic envelope. When heated, the blowing agent evaporates to increase the internal pressure, while the shell softens, resulting in a significant expansion of the microspheres, usually 2 to 5 times their diameter.

Thermoplastic microspheres can be used in various applications such as non-expanded or pre-expanded. Examples of products in which dry pre-expanded microspheres (essentially free of water) are used are as a sensitizer in emulsion explosives and as a light load in solvent-based paints and various thermosetting materials such as cultured marble, polyester putty and wood artificial. In many products, such as water-based paints and coatings, thermal printing papers, porous ceramics and emulsion explosives, wet pre-expanded microspheres are used, usually as an aqueous suspension.

The transport of pre-expanded microspheres requires significant space, so that the unexpanded microspheres for the expanded microspheres are often transported to the end user and expanded in situ. The microspheres can then expand near or directly in a process to produce the final product, e.g. eg, any of those mentioned above.

Several methods and devices have been developed to expand thermoplastic microspheres.

US 5484815 and US 7192989 describe suitable methods and devices for expanding dry microspheres.

JP 2005 254213 describes an apparatus comprising a reactor tube in which the microcapsules are heated to an expansion temperature and in which the aqueous suspension of unexpanded expandable microcapsules is forcedly fed and in which steam is also fed at high steam temperature by applying a back pressure that exceeds the vapor pressure. After heating as it passes through the tube at a certain rate of passage, the heat expandable microcapsules are discharged into the air and expanded.

US 4513106 describes a suitable method and device for expanding microspheres in an aqueous suspension by introducing steam into the suspension in a pressure zone in an amount sufficient to heat the microspheres and expand them at least partially, followed by allowing partially expanded microspheres to leave the pressure zone under a pressure cup so the microspheres expand further and accelerate in a current with a velocity of at least 1 m / s.

WO03 / 051793 describes an apparatus that is suitable for receiving a suspension of unexpanded expandable polymer microspheres that are mixed with steam to cause thermal expansion of the microspheres and to provide a resulting stream of wet expanded microballoons.

In the reaction tube, a motive fluid in the form of gas is used to propel the suspension of microspheres that come into contact with a vapor stream. While the steam generator, the steam duct, the suspension tank and the fluid duct are in fluid communication with the treatment area, there seems to be no back pressure generator in the apparatus.

An advantage of expanding the microspheres in an aqueous suspension is that dusting is avoided. However, it is desirable to further improve the existing technology of expanding microspheres in a suspension.

An object of the present invention is to provide a method and a device for expanding microspheres in a suspension without the need to introduce additional water.

It is another object of the invention to provide a method and a device for expanding microspheres in a suspension that is flexible with respect to which liquid is used for the suspension.

It is a further object of the invention to provide a method and a device for expanding microspheres in a suspension that is flexible with respect to the means for heating the microspheres.

It is still a further object of the invention to provide a method and device for expanding microspheres in a suspension with low risk of agglomeration of the microspheres.

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It is still a further object of the invention to provide a method and device for expanding microspheres in a suspension that can also be used for a wide range of microsphere grades that have varying expansion temperatures.

According to the invention, it has been found that it is possible to achieve these and other objects by a method and a device according to the appended claims.

More specifically, the invention relates to a method for the preparation of expanded thermoplastic microspheres from thermoplastic thermoplastic expandable microspheres comprising a thermoplastic polymeric shell encapsulating a blowing agent, said method comprising:

(a) feeding a suspension of such expandable thermoplastic microspheres in a liquid medium in a heating zone;

(b) heating the suspension in the heating zone, without direct contact with any fluid heat transfer medium, so that the expandable microspheres reach at least a temperature at which they have begun to expand at atmospheric pressure and maintaining a pressure in the heating zone sufficiently high so that the microspheres of the suspension do not expand completely; Y,

(c) remove the suspension of expandable microspheres from the heating zone to an area with a sufficiently low pressure for the microspheres to expand.

The invention further relates to a device for expanding thermally expandable thermoplastic microspheres that comprise a thermoplastic polymer shell that encapsulates a blowing agent, said device comprising a heating zone that has an inlet and an outlet and that is capable of supporting a pressure of at least 4 bars, means for feeding a suspension of expandable thermoplastic microspheres not expanded in a liquid medium in the heating zone and capable of generating a pressure of at least 4 bars in the heating zone; and means for heating the suspension of expandable microspheres at a temperature of at least 60 ° C without direct contact with any fluid heat transfer medium.

Thermoplastic thermoplastic microspheres that are not expanded will be referred to as expandable microspheres. The particle size of the expandable microspheres can vary within wide limits and can be selected with respect to the desired properties of the product in which they are used. In the majority of cases, the preferred median volumetric diameter, determined by laser light scattering in a Malvern Mastersizer Hydro 2000 SM apparatus in wet samples, is 1 pm to 1 mm, preferably 2 pm to 0.5 mm and particularly from 3 pm to 100 pm. The diameter of the microspheres increases in expansion, for example by a factor of 2 to 5.

The liquid medium of the expandable microsphere suspension can be any liquid that is inert with respect to the microspheres and can withstand the temperature at which the suspension is heated. In many cases, water or a water-based liquid is preferred, thus forming an aqueous suspension, but depending on the intended use of the expanded microspheres, organic liquids may also be preferred for the suspension, such as at least one of vegetable oil. , mineral oil and glycerol, whose organic liquids may be free of water. Since it is not necessary to add steam or water in any other way to the suspension in the method of the invention, it is possible to prepare a suspension of expanded microspheres free of water that can be used directly in applications where water is not desired. In addition, since it is not necessary to add any other fluid media to the suspension, it is possible to prepare a suspension of expanded microspheres having a high and controlled solids content.

In the majority of commercial methods of production of expandable microspheres, they are usually obtained first in an aqueous suspension, and said suspension can be used directly in the method of the invention, optionally after dilution or dehydration to a desired microsphere content. On the other hand, such an aqueous suspension can be dried to obtain essentially water-free microspheres that can be used to prepare a suspension in an organic liquid.

The content of expandable microspheres in the suspension depends on what is desired for the product obtained after expansion. The upper limit is limited by the pumping capacity of the suspension and by the portability of the suspension through the heating zone. In most cases, the content of expandable microspheres is suitably from 5 to 50% by weight, preferably from 10 to 40% by weight and most preferably from 15 to 30% by weight.

The suspension of expandable microspheres flows through the heating zone which may be constituted by any vessel, tubena or tube provided with an inlet and an outlet and that supports the pressure maintained therein. The means for heating the suspension therein can be, for example, a fluid heat transfer medium that is not in direct contact with the suspension, electric or microwave heating elements. For example, the heating zone may be a heat exchanger comprising at least one tubena or tube surrounded by a heat transfer means that is not in direct contact with the

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expandable microsphere suspension. A heat exchanger may comprise, for example, several preferably parallel tubenas or tubes, for example 2 to 10 or 3 to 7 tubenas or tubes, preferably connected to a common inlet and a common outlet. It is also possible to have only one tube or tube. The use of a single tubena or tube (ie, only one) implies the advantage of reducing the risk of irregular flow distribution caused by partial clogging in one of several parallel tubenas. Such a single tube or tube is preferably surrounded by a heat transfer medium, such as hot water, preferably located in a container or tank containing the heat transfer medium.

The heat transfer medium may be any suitable fluid medium such as hot water, steam or oil. Alternatively, heat can be provided by electric heating elements, e.g. eg, inside or outside the heating zone or on its walls, or any combination thereof. As an additional alternative, heating can be provided by electromagnetic radiation such as microwaves.

By means of the invention it is possible to expand the degrees of microspheres that require a higher temperature than that which can be achieved practically by means of water vapor, e.g. eg, using electric heating elements or hot oil as heat transfer medium. For example, it is possible to expand microspheres that require temperatures above 200 ° C. It is also possible or can expand microspheres that can collapse or otherwise be damaged at too high temperatures using a heat transfer medium having a comparatively low temperature, for example from 60 to 100 ° C, such as hot water.

The container or at least one tube or tube in which the suspension of expandable microspheres flows is preferably of a thermally conductive material such as steel or copper, in particular if the heating of the suspension is carried out by means of a fluid transfer medium of heat or electric heating elements. If the heating is provided by electromagnetic radiation, the container or at least one tubena or tube is preferably of a permeable material for such radiations, such as various types of polymeric materials.

In a heat exchanger comprising at least one tubena or tube, said at least one tubena or tube may, for example, each have an internal diameter of 2 to 25 mm or more preferably the internal diameter is 4 to 15 mm or most preferably 6 to 12 mm. The thickness of the walls of at least one tubena or tube is suitably 0.5 to 3 mm, preferably 0.7 to 1.5 mm.

If the heating is carried out by means of electric heating elements, said elements may be, e.g. eg, at least one tubena or tube, for example a single tubena or tube. Said tubena or tube can have, for example, an inner diameter of 20 to 80 mm or 35 to 65 mm. For example, an electric heating element may be provided in the center within a pipe or tube for the suspension of expandable microspheres to flow in the space around that heating element. Such an electric heating element can itself be a tubena or tube with the primary electric heating source therein, so that heat is transferred through the wall to the suspension flowing in the separation. Preferably, electric heating elements are provided both inside and outside the at least one tubena or tube.

The optimum dimensions and the capacity of the means to heat the suspension are determined by the flow rate of the suspension, the concentration of the suspension and the temperature of the incoming suspension and should be sufficient for the suspension to reach a sufficiently high temperature for the microspheres expand when the pressure decreases after passing the exit of the heating zone. This temperature is always higher than the volatilization temperature of the blowing agent of the specific microsphere.

The expandable microsphere suspension is fed to the heating zone through its inlet, preferably by means of a pump that provides a sufficiently high pressure in the heating zone so that the microspheres do not fully expand inside. The microspheres can partially expand within the heating zone, e.g. eg, at a volume of 10 to 80% or 20 to 70% of the volume after the expansion completed outside the heating zone, but it can also be prevented from expanding at all within the heating zone. Examples of suitable pumps include hydraulic diaphragm pumps, piston pumps, screw pumps (for example, eccentric screw pumps), gear pumps, rotary lobe pumps, centrifugal pumps, etc. Hydraulic diaphragm pumps are particularly preferred. Preferably, the pump also creates the force to transport the suspension through the heating zone to its exit. The device may also be provided with a conduit for transporting the suspension of expandable microspheres to the pump, for example from a tank containing the suspension.

In order to maintain a sufficiently high pressure in the heating zone, the expandable microsphere suspension is extracted from the heating zone through an outlet thereof creating a pressure coffe corresponding to the pressure difference between the interior of the heating zone and the outside of the heating zone. The pressure cup can be created by any suitable means, such as a restriction of the flow area, for example a valve, a nozzle or any other type of narrow passage. The outlet of the heating zone may be, for example, a preferably insulated pipe or tube that optionally has a restriction of the flow area at its end, such as an opening having a diameter of 0.9 to 0.05 times or from

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0.5 to 0.05 times, preferably 0.3 to 0.1 times the inside diameter of said tubena or tube. However, a restriction of flow area or any other special means is not necessary, since the pressure layer created by an outlet having the same flow area as the heating zone is usually sufficient to avoid termination of the expansion of the microspheres within the heating zone. The tubena or tube can be nested or flexible, which in the latter can easily be directed to a desired exit point for the microspheres without moving the entire device.

The exact pressure required in the heating zone depends on the temperature and the type of microsphere. Preferably, the pressure maintained in the heating zone is at least 4 bars, most preferably at least 10 bars. The upper limit is determined by practical considerations and can be, for example, up to 40 bars or up to 50 bars. The heating zone should preferably be able to withstand such pressure.

The temperature of the expandable microspheres in the heating zone is usually essentially the same as the temperature of the suspension therein. The exact temperature at which the suspension is heated depends on the degree of the microspheres. For the majority of the microsphere grades, the temperature is preferably in the range of 60 to 160 ° C, preferably 80 to 160 ° C or 100 to 150 ° C, although higher temperatures, such as 200 ° C or even 250 ° C or more may be necessary for some degrees of microspheres. The means for heating the suspension should preferably be able to heat the suspension at such temperature.

A flow of a suspension of expandable microspheres is conveyed in the heating zone from the inlet to the outlet and is heated under pressure to a temperature high enough for the microspheres to optionally expand partially therein and at least to expand when the pressure drops to the exit of the heating zone and they enter the zone with a sufficiently low pressure. The pressure in that area is usually essentially atmospheric pressure but can be kept higher or lower depending on the temperature of the microspheres. In this phase, the microspheres are generally also cooled by the surrounding air in that area. The average residence time of the microspheres in the heating zone is preferably long enough to ensure that a sufficiently high temperature of the suspension is reached and maintained for subsequent expansion. In order to ensure the production of a high and uniform quality, the device may optionally be provided in addition to a pulsation damper that stabilizes the flow of the suspension.

When the expansion continues or begins in the pressure chamber at the exit of the heating zone, the flow of microspheres is also significantly accelerated. At the same time, the microspheres automatically cool to a temperature so low that the expansion stops, forming the point where the expansion is completed. In order to optimize the disintegration of the microspheres and avoid agglomeration, it is preferred that the pressure coffee takes place as short as possible in the direction of flow.

As the decay and cooling of the microspheres after passing the pressure coffee at the exit of the heating zone occur rapidly, the expanded microspheres are usually substantially free of agglomerates. The expanded microspheres can be used immediately for the intended purpose or can be packaged in plastic bags, cartridges or other suitable containers.

The method and device of the invention are particularly useful for in situ expansion in the production of,

eg, emulsion explosives, paint, polyester putty, artificial wood formulations based on polyester, polyurethane or epoxy, epoxy-based culture marble, porous ceramics, plasterboard, carcass floor coverings, elastomers , crack fillings, sealants, adhesives, phenolic resins, stucco, cable insulating compound, modeling clay, microcellular polyurethane foams, thermal printing paper coatings and other types of coatings. The flow of expanded microspheres leaving the device can then be added directly to the production lines of such products. For example, the flow of expanded microspheres can be added directly in the emulsion flow during the production of emulsion explosives or directly in the emulsion flow during the filling of a perforation with emulsion explosives

coming from a truck. In the latter case, explosives can be sensitized at the mining site and

transported without sensitizing the mine.

The method and the expansion device according to the invention can be used for all known types of expandable thermoplastic microspheres, such as those sold under the trademark Expancel ™. Useful expandable thermoplastic microspheres and their preparation are also described in, for example, US Pat. 3615972, 3945956, 4287308, 5536756, 6235800, 6235394 and 6509384, 6617363 and 6984347, in US Patent Publications US 2004/0176486 and 2005/0079352, in EP 486080, EP 566367, EP 1067151, EP 1230975, EP 1288272, EP 1598405, EP 1811007 and EP 1964903, in WO 2002/096635, WO 2004/072160, WO 2007/091960, WO 2007/091961 and WO 2007/142593, and in Japanese patents open for public inspection No. 1987-286534 and 2005-272633.

Suitable thermoplastic microspheres preferably have a thermoplastic shell made of polymers or copolymers obtainable by polymerization of various ethylenically unsaturated monomers, which may be nitrile-containing monomers, such as acrylonitrile, methacrylonitrile, alpha-chloroacrylonitrile, alpha-ethoxycritonitrile

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fumaronitrile, crotonitrile, acrylic esters such as methyl acrylate or ethyl acrylate, methacrylic esters such as methyl methacrylate, isobornyl methacrylate or ethyl methacrylate, vinyl halides such as vinyl chloride, vinylidene halides such as vinylidene chloride, vinylpyridine, vinylic esters such as vinyl acetate, styrenes such as styrene, halogenated styrenes or alpha-methyl styrene, or dienes such as butadiene, isoprene and chloroprene. Mixtures of the monomers mentioned above can also be used.

Sometimes it may be desirable that the monomers for the polymeric sheath also comprise cross-functional multifunctional monomers, such as one or more of divinylbenzene, ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate , propylene glycol di (meth) acrylate, 1,4-butanediol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, glycerol di (meth) acrylate, 1,3 (meth) acrylate -butanediol, neopentyl glycol di (meth) acrylate, 1,10-decanediol di (meth) acrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, hexa (meth) pentaerythritol acrylate, di (met ) dimethylol tricyclodecane acrylate, tri (meth) triallylformal acrylate, allyl methacrylate, trimethylolpropane tri (meth) acrylate, trimethylolpropane triacrylate, trimethyl diol methacrylate, di (meth) acrylate PEG No. 200 PEG (meth) acrylate No. 400, PEG di (meth) acrylate No. 600, 3-acryloyloxyglycol monoacrylate, triacryl-formal or isocyan trialyl ato, triallyl isocyanurate, etc. If present, said crosslinking monomers preferably constitute 0.1 to 1% by weight, most preferably 0.2 to 0.5% by weight of the total amounts of monomers for the polymer wrap. Preferably, the polymeric shell constitutes 60 to 95% by weight, most preferably 75 to 85% by weight, of the total microsphere.

The softening temperature of the polymeric shell, which normally corresponds to its glass transition temperature (Tg), is preferably in the range of 50 to 250 ° C, or 100 to 230 ° C.

The blowing agent in a microsphere is normally a liquid having a boiling temperature no greater than the softening temperature of the thermoplastic polymer shell. The blowing agent, sometimes also referred to as a foaming or blowing agent, can be at least one hydrocarbon such as n-pentane, isopentane, neopentane, butane, isobutane, hexane, isohexane, neohexane, heptane, isoheptane, octane and isooctane, or mixtures of the same. Other types of hydrocarbons, such as petroleum ether and chlorinated or fluorinated hydrocarbons, such as methyl chloride, methylene chloride, dichloroethane, dichloroethylene, trichloroethane, trichlorethylene, trichlorofluoromethane, etc. can also be used. Particularly preferred blowing agents comprise at least one of isobutane, isopentane, isohexane, cyclohexane, isooctane, isododecane and mixtures thereof, preferably isooctane. The blowing agent suitably composes 5 to 40% by weight of the microsphere.

The boiling point of the atmospheric pressure blowing agent can be within a wide range, preferably from -20 to 200 ° C, most preferably from -20 to 150 ° C, and most preferably from -20 to 100 ° C .

The temperature at which the expandable microspheres begin to expand depends on a combination of the blowing agent and the polymeric shell and the microspheres having various expansion temperatures are commercially available. The temperature at which the microspheres begin to expand at atmospheric pressure is called Tcomienzo. The expandable microspheres used in the present invention preferably have a T-start of 40 to 230 ° C, most preferably 60 to 180 ° C.

The attached figure illustrates an embodiment of the invention.

The figure shows a device comprising a hydraulic diaphragm pump 1 connected to a heat exchanger 4 (which forms a heating zone) and a pulsation damper 2. The heat exchanger 4 is provided with an inlet 10 and an outlet 8 in the form of a tubena provided with a restriction of the flow area at the end in the form of a nozzle. The heat exchanger further comprises one or a plurality of tubes (not shown) surrounded by a heat transfer medium (not shown) such as hot water, steam or oil. The device further comprises a manometer 3, a safety valve 5, a control valve 6, a thermometer 7 and a 3-way valve 9.

The device is operated by pumping a suspension of expandable microspheres, e.g. e.g., from a suspension tank (not shown), by means of the hydraulic diaphragm pump 1 through the heat exchanger 4, in which it is heated by the heat transfer means at a temperature at which the microspheres begin to expand or at least have begun to expand at atmospheric pressure. The hydraulic diaphragm pump creates sufficient pressure to transport the suspension through heat exchanger 4 and prevent full expansion of the microspheres inside. The hot suspension flows into the open air through the outlet 8, optionally provided with a restriction of the flow area, creating a pressure coffee at atmospheric pressure, resulting in rapid expansion and cooling of the microspheres in the open air. The pulsation dampener 2 inhibits fluctuations in the flow of the suspension from the hydraulic diaphragm pump 1. The pressure and temperature in the heat exchanger can be controlled by the manometer 3 and the thermometer 7, respectively. The equipment can be cleaned by exchanging the suspension of expandable microspheres for, for example, washing water with the help of the 3-way valve 9 before the pump 1. The flow and pressure of the heat transfer medium used in the exchanger of heat 4 is regulated by the control valve 6.

Example 1:

AkzoNobel Expancel ™ 051-40 expandable microspheres were expanded using a device according to the attached Figure. An aqueous suspension of 15% by weight microspheres was pumped at a temperature of 20 ° C at a rate of 3 liters / min through the heat exchanger comprising seven tubes, each with 5 an inner diameter of 10 mm, a external diameter of 12 mm and a length of 1.95 meters, surrounded by hot steam as a means of heat transfer. The pump generated a pressure of 30 bars that was maintained inside the heat exchanger and the thermal energy transferred by the steam sufficient to heat the suspension to 130 ° C. The microspheres left the heat exchanger through the outlet provided with a nozzle that feeds a 1.5 mm open-air opening of 20 ° C and expanded to reach a density of 22 g / dm3. The expanded microsphere product 10 had a solids content of 15% by weight and the microscopic investigation showed that the product was completely free of agglomerates.

Example 2

The AkzoNobel Expancel ™ 031 expandable microspheres were expanded using a device comprising a single 5.8 m long copper tube located in a tank filled with hot water maintained at a temperature of 100 ° C. The copper tubena has an inner diameter of 6.3 mm and an outer diameter of 7.8 mm, but does not fear any restriction of flow area. A 20% by weight aqueous microsphere suspension was pumped at a temperature of 20 ° C with a diaphragm pump at a rate of 80 liters / hour through the copper tube surrounded by hot water as a heat transfer medium. The diaphragm pump generated a pressure of 6 bars. The microspheres left the heat exchanger of the copper tube through the outlet and 20 reached after the final expansion a density of 24 g / dm3. The expanded microsphere product had a solids content of 20% by weight and the microscopic investigation showed that the product was essentially free of agglomerates.

Claims (15)

5 10 fifteen twenty 25 30 35 40 Four. Five fifty 1. A method for the preparation of expanded thermoplastic microspheres from thermally expandable thermoplastic expandable microspheres comprising a thermoplastic polymer shell encapsulating a blowing agent, said method comprising: (a) feeding a suspension of such expandable thermoplastic microspheres in a liquid medium in a heating zone; (b) heating the suspension in the heating zone, without direct contact with any fluid heat transfer medium, so that the expandable microspheres reach at least a temperature at which they have begun to expand at atmospheric pressure and maintaining a pressure in the heating zone high enough so that the microspheres in the suspension do not expand completely; Y, (c) remove the suspension of expandable microspheres from the heating zone to an area with a sufficiently low pressure for the microspheres to expand. 2. A method according to claim 1, wherein the pressure in the heating zone is maintained at 5 to 50 bar. 3. A method according to any one of claims 1-2, wherein the suspension of expandable microspheres is heated in the heating zone at a temperature of 60 to 160 ° C. 4. A method according to any one of claims 1-3, wherein the suspension of expandable microspheres flows through a heating zone which is a heat exchanger comprising at least one tubena or tube surrounded by a transfer means of heat that is not in direct contact with the suspension of expandable microspheres. 5. A method according to claim 4, wherein at least one tubena or tube each has an inner diameter of 2 to 25 mm. 6. A method according to any one of claims 1-3, wherein the heat is provided by electric heating elements. 7. A method according to any one of claims 1-6, wherein the suspension of expandable microspheres is extracted from the heating zone through an outlet thereof creating a pressure coffe corresponding to the pressure difference between the inside the heating zone and outside the heating zone. 8. A method according to claim 7, wherein the outlet is provided with a restriction of flow area to create the pressure coffer. 9. A method according to any one of claims 1-8, wherein the expandable microsphere suspension is removed from the heating zone to an atmospheric pressure zone. 10. A method according to any one of claims 1-9, wherein the expandable microsphere suspension is fed to the heating zone by means of a pump that provides a sufficiently high pressure in the heating zone so that the microspheres do not expand completely inside. 11. A device for the expansion of thermoplastic thermoplastic expandable microspheres comprising a thermoplastic polymer shell encapsulating a blowing agent, said device comprising a heating zone having an inlet and an outlet and which is capable of withstanding a pressure of at least 4 bars, means for feeding a suspension of expandable thermoplastic microspheres not expanded in a liquid medium in the heating zone and capable of generating a pressure of at least 4 bars in the heating zone; and means for heating the suspension of expandable microspheres at a temperature of at least 60 ° C without direct contact with any fluid heat transfer medium. 12. A device according to claim 11, wherein the outlet is provided with a restriction of sufficient flow area to create a pressure coffe corresponding to the pressure difference between the inside of the heating zone and outside the zone of heating. 13. A device according to any one of claims 11-12, wherein the heating zone is a heat exchanger comprising at least one tubena or tube surrounded by a heat transfer means that is not in direct contact with the expandable microsphere suspension. 14. A device according to any one of claims 11-13, wherein the heating zone comprises a single tubena or tube surrounded by a heat transfer means that is not in direct contact with the expandable microsphere suspension. 15. A device according to any one of claims 11-12, wherein the heating zone comprises at least one tubena or tube and electric heating elements provided inside and / or outside said at least one tubena or tube.